The hepatitis C virus (HCV), a member of the hepacivirus genera within the Flaviviridae family, is the leading cause of chronic liver disease worldwide (Boyer, N. et al. J. Hepatol. 2000, 32, 98-112). Consequently, a significant focus of current antiviral research is directed toward the development of improved methods for the treatment of chronic HCV infections in humans (Ciesek, S., von Hahn T., and Manns, M P., Clin. Liver Dis., 2011, 15, 597-609; Soriano, V. et al, J. Antimicrob. Chemother., 2011, 66, 1573-1686; Brody, H., Nature Outlook, 2011, 474, S1-S7; Gordon, C. P., et al., J. Med. Chem. 2005, 48, 1-20; Maradpour, D., et al., Nat. Rev. Micro. 2007, 5, 453-463).
Virologic cures of patients with chronic HCV infection are difficult to achieve because of the prodigious amount of daily virus production in chronically infected patients and the high spontaneous mutability of HCV (Neumann, et al., Science 1998, 282, 103-7; Fukimoto, et al., Hepatology, 1996, 24, 1351-4; Domingo, et al., Gene 1985, 40, 1-8; Martell, et al., J. Virol. 1992, 66, 3225-9). HCV treatment is further complicated by the fact that HCV is genetically diverse and expressed as several different genotypes and numerous subtypes. For example, HCV is currently classified into six major genotypes (designated 1-6), many subtypes (designated a, b, c, and so on), and about 100 different strains (numbered 1, 2, 3, and so on).
HCV is distributed worldwide with genotypes 1, 2, and 3 predominate within the United States, Europe, Australia, and East Asia (Japan, Taiwan, Thailand, and China). Genotype 4 is largely found in the Middle East, Egypt and central Africa while genotype 5 and 6 are found predominantly in South Africa and South East Asia respectively (Simmonds, P. et al. J. Virol. 84: 4597-4610, 2010).
The combination of ribavirin, a nucleoside analog, and interferon-alpha (α) (IFN), is utilized for the treatment of multiple genotypes of chronic HCV infections in humans. However, the variable clinical response observed within patients and the toxicity of this regimen have limited its usefulness. Addition of a HCV protease inhibitor (telaprevir or boceprevir) to the ribavirin and IFN regimen improves 12-week post-treatment virological response (SVR12) rates substantially. However, the regimen is currently only approved for genotype 1 patients and toxicity and other side effects remain.
The use of directing acting antivirals to treat multiple genotypes of HCV infection has proven challenging due to the variable activity of antivirals against the different genotypes. HCV protease inhibitors frequently have compromised in vitro activity against HCV genotypes 2 and 3 compared to genotype 1 (See, e.g., Table 1 of Summa, V. et al., Antimicrobial Agents and Chemotherapy, 2012, 56, 4161-4167; Gottwein, J. et al, Gastroenterology, 2011, 141, 1067-1079). Correspondingly, clinical efficacy has also proven highly variable across HCV genotypes. For example, therapies that are highly effective against HCV genotype 1 and 2 may have limited or no clinical efficacy against genotype 3. (Moreno, C. et al., Poster 895, 61st AASLD Meeting, Boston, Mass., USA, Oct. 29-Nov. 2, 2010; Graham, F., et al, Gastroenterology, 2011, 141, 881-889; Foster, G. R. et al., EASL 45th Annual Meeting, Apr. 14-18, 2010, Vienna, Austria.) In some cases, antiviral agents have good clinical efficacy against genotype 1, but lower and more variable against genotypes 2 and 3. (Reiser, M. et al., Hepatology, 2005, 41, 832-835.) To overcome the reduced efficacy in genotype 3 patients, substantially higher doses of antiviral agents may be required to achieve substantial viral load reductions (Fraser, I P et al., Abstract #48, HEP DART 2011, Koloa, Hi., December 2011.)
Antiviral agents that are less susceptible to viral resistance are also needed. For example, resistance mutations at positions 155 and 168 in the HCV protease frequently cause a substantial decrease in antiviral efficacy of HCV protease inhibitors (Mani, N. Ann Forum Collab HIV Res., 2012, 14, 1-8; Romano, K P et al, PNAS, 2010, 107, 20986-20991; Lenz O, Antimicrobial agents and chemotherapy, 2010, 54, 1878-1887.)
In view of the limitations of current HCV therapy, there is a need to develop more effective anti-HCV therapies. It would also be useful to provide therapies that are effective against multiple HCV genotypes and subtypes.